Using the localStorage object, the storage event and the postMessage() API, it is possible for browser windows to discover each other and to communicate with each other.
Crosscasting is a small Dojo package that publishes Dojo PubSub events to other browser windows that are running the Crosscasting code and are active within the same domain. Crosscasting of course stands for cross-window broadcasting.
Try it out by opening a new window. Fill in your name, a message and hit submit!
View the source of this page to see how Crosscasting is used, and have a look at crosscast.js.
Currently this only seems to work in the latest WebKit nightly builds.
Have fun! — Mark Wubben / @novemberborn.